Particle beam devices of the type mentioned above often have deflection systems which can be used to deflect the particle beam in the object plane substantially perpendicularly to the direction of propagation of the particle beam. By detecting the interaction products of the particle beam with a sample surface arranged in the object plane in a manner dependent on the deflection of the particle beam, it is then possible to generate an image of the sample surface. As an alternative or in addition thereto, a process gas which can be activated by the particle beam can be fed to the sample surface, with the aid of which gas, then in the regions in which the particle beam impinges on the sample surface, the sample surface is locally etched or material from the process gas is deposited on the sample surface.
Furthermore, it is possible for a particle-sensitive layer previously applied to the sample surface to be locally exposed with the aid of the particle beam and then to be patterned by further methods.
The particle beam is generated in a particle beam generator and focused by an objective lens in the object plane. The particle beam focused there is often and also hereinafter also designated as a particle probe.
The movement of the particle probe is generally effected by a deflection of the particle beam by a magnetic field generated with the aid of coils, and/or with the aid of an electric field generated with the aid of electrodes. The coils of magnetic deflection systems are often embodied as air-core coils which can be arranged outside the vacuum tube and which enable the particle beam or the particle probe to be deflected sufficiently rapidly.
For focusing the particle beam or for generating the particle probe, it is possible to use an objective lens which is likewise formed by magnetic and/or electric fields. The objective lens is usually operated with a focal length that is as short as possible, in order to achieve a resolution that is as good as possible. On account of the small focal length of the objective lens, the working distance between the objective lens and the object plane is very small and generally amounts to only a few millimeters to a few centimeters. On account of the small structural space between the objective lens and the object plane, the deflection systems are generally arranged on the source side of the objective lens.
If, for the deflection of the particle beam, a single simple deflection system is used on the source side or within the objective lens, the particle beam runs through the objective lens with different degrees of obliqueness depending on the intensity of the deflection of the particle beam, as a result of which image aberrations dependent on the deflection of the particle beam arise. In order that such image aberrations dependent on the deflection angle are avoided or kept small, so-called double deflection systems are often used, which have two individual deflection systems arranged at a distance from one another in the direction of the optical axis of the particle beam or the objective lens. Through suitable combination of the deflections of two deflection systems arranged serially one behind the other, it is possible to shift the position of a virtual tilting point along the particle-optical axis, wherein the deflection appears virtually as if produced by tilting about the tilting point. As a result, it is possible, for example, to produce a virtual tilting point for the deflection in a plane which leads to a minimization of the additional image aberrations dependent on the intensity of the deflection, even if the corresponding plane is inaccessible for the arrangement of a deflection system.
The adjustment of the deflection fields of the two deflection systems arranged serially one behind the other along the optical axis and of the currents and/or voltages used for generating the deflection fields is usually effected in the course of adjusting the particle beam device in a manner dependent on the objective lens specifically used. In this case, the adjustment is generally effected in such a way that the additional image aberrations generated by the deflection, which are then dependent on the intensity of the deflection, are minimal The adjustment data correspondingly obtained in the course of adjusting the particle beam device are then stored and no longer changed during the subsequent operation of the particle beam device.
U.S. Pat. No. 6,809,322 discloses a particle beam device having three deflection systems arranged serially one behind another. What is intended to be achieved via the three deflection systems arranged serially one behind another is that the image field maximally scanned with the particle beam in the object plane is not trimmed, or is trimmed only as little as possible, by a pressure stage aperture arranged between the objective lens and the object plane.
In some particle beam devices from the applicant it is possible to operate them in a so-called “fish-eye mode”. In this “fish-eye mode”, two deflection systems arranged serially one behind the other produce deflections in the same direction. The particle beam then runs off-axis to a very great extent in the case of a deflection in the objective lens, which leads to severe off-axis aberrations. The image recorded in this “fish-eye mode” therefore has very severe aberrations dependent on the deflection angle, but at the same time makes it possible to generate a very large overview image of the entire sample, or of the entire interior of the sample chamber. This “fish-eye mode” is achieved by virtue of the fact that, upon changeover to this “fish-eye mode”, the polarity of the deflection system arranged nearer to the objective lens is changed over relative to the normal operation mode.
In some other particle beam devices from the applicant, it is possible to operate them in a so-called “tilting raster mode”. In this “tilting raster mode”, two deflection systems arranged serially one behind the other produce deflections in the same direction, but in a somewhat different ratio. The particle beam then still runs off-axis in the case of a deflection in the objective lens, and is then directed by the objective lens again to that point on the sample on which the particle beam impinges even without deflection. The deflection in the two deflection systems is therefore effected in the manner as if the deflected particle beam came from the particle source. It is thus possible to realize measurements concerning the crystal microstructure of the sample, since other interaction products arise depending on the orientation of the impinging particle beam. This “tilting raster mode” is achieved by virtue of the fact that, upon changeover to this “tilting raster mode”, a suitable resistor-inductor combination is connected in parallel with the deflection system arranged nearer to the objective lens, relative to the normal operation mode.